The presence and persistence of pathogenic fungal infections seen in patients and animals but also in plant crops can be mainly attributed to the selective pressure of broad-spectrum anti-fungals and the general lack of efficacy of anti-fungal agents, which are available at present.
In humans and animals, systemic fungal infections such as invasive candidiasis and invasive aspergillosis may be caused by a variety of fungal pathogens, for example, the virulent Candida species C. albicans, C. tropicalis and C. krusei and the less virulent species C. parapsilosis and Torulopsis glabrata (the latter sometimes referred to as Candida glabrata). Although C. albicans was once the most common fungal isolate obtained from intensive care units, later studies have indicated that C. tropicalis, C. glabrata, C. parapsilosis and C. krusei now account for about half of such isolates. The rise of non-albicans species implies the emergence of Candida species resistant to conventional antifungal therapy.
Traditionally, C. albicans, C. tropicalis and C. parapsilosis have been treated by the antifungal agent amphotericin B, regarded as the “gold standard” of systemic antifungal therapy. Unfortunately, amphotericin B is itself highly toxic and its use is tempered by side effects including chills, fever, myalgia or thrombophlebitis. Other anti-fungal agents include the oral azole drugs (miconazole, ketoconazole, itraconazole, fluconazole) and 5-fluorocytosine. However, fungal species such as C. krusei and T. glabrata are resistant to fluconazole, and these species often occur in patients where this drug has been administered prophylactically. Furthermore, fluconazole-resistant strains of C. albicans have also been reported. Thus, despite the advances made in therapeutic anti-fungal drugs, the need for effective agents for treatment of fungal infections remains acute.
In agriculture, crop protection relies heavily on the use of pesticides, which are applied to the crops by spraying them onto the crop, applying during watering of the crops or incorporating them into the soil. Pesticides are often organic chemical molecules and their repeated application to crops poses toxicity threats to both agricultural workers during handling and to the environment, due to spray drift, persistence in the soil or washing off into surface or ground water. It would be advantageous to be able to use alternative compounds that are less toxic to humans and the environment, but that at the same time provide effective control of plant pests. Proteinaceous pesticides with specificity against a certain plant pest target may be very advantageous in this respect, as they are expected to be short-lived in the environment and to have less toxic off-target effects. However, there are only a few proteinaceous or peptidergic pesticides known. Some examples are Bt toxins, lectins, defensins, fabatins, tachyplesin, magainin, harpin (see WO2010019442), pea albumin 1-subunit b (PA1b). However, these proteinaceous pesticides are either small peptides with compact structures, stabilized by several disulphide bridges, or are larger proteins (>300 amino acids) that occur in crystalline form (cry toxins). It is indeed known in the field of agriculture that biologicals and, in particular, proteins, are challenging structures for developing pesticides, as they generally have far too little stability to maintain their pesticidal function in an agrochemical formulation, in particular, for applications in the field.